.Dd June 20, 2019
.Dt dyld 3
.Sh NAME
.Nm _dyld_image_count,
.Nm _dyld_get_image_header,
.Nm _dyld_get_image_vmaddr_slide,
.Nm _dyld_get_image_name,
.Nm _dyld_register_func_for_add_image,
.Nm _dyld_register_func_for_remove_image,
.Nm NSVersionOfRunTimeLibrary,
.Nm NSVersionOfLinkTimeLibrary
.Nm _NSGetExecutablePath
.Sh SYNOPSIS
.In mach-o/dyld.h
.Ft uint32_t
.Fo _dyld_image_count
.Fa "void"
.Fc
.Ft const struct mach_header*
.Fo _dyld_get_image_header
.Fa "uint32_t image_index"
.Fc
.Ft intptr_t
.Fo _dyld_get_image_vmaddr_slide
.Fa "uint32_t image_index"
.Fc
.Ft const char*
.Fo _dyld_get_image_name
.Fa "uint32_t image_index"
.Fc
.Ft void
.Fo _dyld_register_func_for_add_image
.Fa "void \*[lp]*func\*[rp]\*[lp]const struct mach_header* mh, intptr_t vmaddr_slide\*[rp]"
.Fc
.Ft void
.Fo _dyld_register_func_for_remove_image
.Fa "void \*[lp]*func\*[rp]\*[lp]const struct mach_header* mh, intptr_t vmaddr_slide\*[rp]"
.Fc
.Ft int32_t
.Fo NSVersionOfRunTimeLibrary
.Fa "const char* libraryName"
.Fc
.Ft int32_t
.Fo NSVersionOfLinkTimeLibrary
.Fa "const char* libraryName"
.Fc
.Ft int
.Fo _NSGetExecutablePath
.Fa "char* buf"
.Fa "uint32_t* bufsize"
.Fc
.Sh DESCRIPTION
These routines provide additional introspection of dyld beyond that provided by
.Fn dlopen
and
.Fn dladdr
.
.Pp
.Fn _dyld_image_count
returns the current number of images mapped in by dyld. Note that using this
count to iterate all images is not thread safe, because another thread
may be adding or removing images during the iteration.
.Pp
.Fn _dyld_get_image_header
returns a pointer to the mach header of the image indexed by image_index.  If 
.Fa image_index
is out of range, NULL is returned.
.Pp
.Fn _dyld_get_image_vmaddr_slide
returns the virtural memory address slide amount of the image indexed by
.Fa image_index.
If
.Fa image_index
is out of range zero is returned.
.Pp
.Fn _dyld_get_image_name
returns the name of the image indexed by
.Fa image_index.
The C-string continues to be owned by dyld and should not deleted.
If 
.Fa image_index
is out of range NULL is returned.
.Pp
.Fn _dyld_register_func_for_add_image
registers the specified function to be called when a new image is added
(a bundle or a dynamic shared library) to the program.  When this function is
first registered it is called for once for each image that is currently part of
the process.  The function is called with the dyld lock held.  This blocks other
threads from using dlopen().  Therefore, the function should do minimal work and
return.
.Pp
.Fn _dyld_register_func_for_remove_image
registers the specified function to be called when an image is removed
(a bundle or a dynamic shared library) from the process.
.Pp
.Fn NSVersionOfRunTimeLibrary
returns the current_version number of the currently loaded dylib 
specifed by the libraryName.  The libraryName parameter would be "bar" for /path/libbar.3.dylib and
"Foo" for /path/Foo.framework/Versions/A/Foo.  This function returns -1 if no such library is loaded.
.Pp
.Fn NSVersionOfLinkTimeLibrary
returns the current_version number that the main executable was linked
against at build time.  The libraryName parameter would be "bar" for /path/libbar.3.dylib and
"Foo" for /path/Foo.framework/Versions/A/Foo.  This function returns -1 if the main executable did not link
against the specified library.
.Pp
.Fn _NSGetExecutablePath
copies the path of the main executable into the buffer
.Fa buf .
The 
.Fa bufsize
parameter should initially be the size of the buffer.  This function returns 0 if the path was successfully copied,
and  *
.Fa bufsize
is left unchanged. 
It returns -1 if the buffer is not large enough, and *
.Fa bufsize
is set to the size required. 
Note that 
.Fn _NSGetExecutablePath 
will return "a path" to the executable not a "real path" to the executable. 
That is, the path may be a symbolic link and not the real file. With deep directories the total bufsize 
needed could be more than MAXPATHLEN.
.Sh SEE ALSO
.Xr dlopen 3
.Xr dladdr 3
.Xr dyld 1
https://developer.apple.com/library/archive/documentation/DeveloperTools/Conceptual/MachOTopics/0-Introduction/introduction.html
